リソースの定義

import { AttributeType, Table } from 'aws-cdk-lib/aws-dynamodb';
import { IFunction, Runtime } from 'aws-cdk-lib/aws-lambda';
import { NodejsFunction } from 'aws-cdk-lib/aws-lambda-nodejs';
import { RemovalPolicy } from 'aws-cdk-lib';
import { Construct } from 'constructs';

export interface HitCounterProps {
  /** the function for which we want to count url hits **/
  downstream: IFunction;
}

export class HitCounter extends Construct {
  /** allows accessing the counter function */
  public readonly handler: IFunction;
  constructor(scope: Construct, id: string, props: HitCounterProps) {
    super(scope, id);

    const table = new Table(this, 'Hits', {
      partitionKey: { name: 'path', type: AttributeType.STRING },
      // Note: プロダクションではDBテーブルは保持することが多いが今回はハンズオンのためDESTROYを指定
      removalPolicy: RemovalPolicy.DESTROY,
    });

    this.handler = new NodejsFunction(this, 'HitCounterHandler', {
      runtime: Runtime.NODEJS_16_X,
      entry: 'lambda/hitcounter.ts',
      environment: {
        DOWNSTREAM_FUNCTION_NAME: props.downstream.functionName,
        HITS_TABLE_NAME: table.tableName,
      },
    });

    // Lambda関数に対してテーブルを読み書き/別のLambdaを実行する権限を付与
    // CDKでは「grant」を利用してリソースに権限を付与できる
    table.grantReadWriteData(this.handler);
    props.downstream.grantInvoke(this.handler);
  }
}